One of the biggest problems that determine the limitation in performance of supercomputers in recent years is power consumption, and the importance of researches relating to the power-saving capability of supercomputers has already been recognized widely. That is, the speed performance per consumed power (Flops/W) has become one barometer for evaluating the supercomputers. Further, in data centers, it is understood that 45% or so of the power consumption by the whole data centers are consumed for cooling, and therefore, a demand for reduction of the power consumption through improvements in cooling efficiency has become strong.
Heretofore, an air-cooling type and a liquid-cooling type have been in use for cooling supercomputers and data centers. The liquid-cooling type is generally recognized to be high in cooling efficiency because of using a liquid that is remarkably superior to air in heat transfer performance. For example, the “TSUBAME-KFC” built by Tokyo Institute of Technology achieved 4.50 G Flops/W by a liquid immersion cooling system using a synthetic oil and acquired the first place in “Supercomputer Green 500 List” announced on November, 2013 and June, 2014. However, because the synthetic oil being high in viscosity is used as the cooling liquid, it is difficult to completely remove, from electronic apparatuses taken out from oil-immersed racks, the oil adhered thereto, and this gives rise to a problem that the maintenance (specifically, adjustment, inspection, repair, replacement and expansion, for example; the same applies hereafter) of the electronic apparatuses is extremely difficult. Furthermore, the occurrence of a problem has been reported that causes a difficulty to arise in practical use because, for example, the synthetic oil in use leaks by corroding a gasket and the like constituting the cooling system in a short period of time.
On the other hand, there has been proposed a liquid immersion cooling system that uses not the synthetic oil causing the aforementioned problems but a cooling liquid of the fluorocarbon-base. Specifically, it is an example that uses a cooling liquid of the fluorocarbon-base (a hydrofluoroether (HFE) compound known as “Novec (trademark of 3M Company; the same applies hereafter) 7100”, “Novec 7200” and “Novec 7300”, brand names of 3M Company) (Patent Literature 1 and Patent Literature 2, for example).